1 . Field of the Invention
This invention relates to a miniature motor, and more particularly to a miniature motor having such a construction that any one of the brushes of the brushgear is adapted to be electrically connected to the motor case.
2 . Description of the Pertinent Prior Art
A miniature motor to which this invention is applied has such a construction that a permanent magnet formed into an arc-segment shape is fixedly fitted in a case made of a metallic material, such as mild steel and formed into a bottomed hollow cylindrical shape; a rotor consisting of an armature and a commutator is rotatably fitted to the case; the open end of the case is engaged with a case cover made of an insulating material; and brushes made of an electrically conductive material are provided on the case cover; power being fed to the armature from brush terminals connected to a power source via the brushes and the commutator.
In d-c miniature motors having the aforementioned construction, for example, miniature motors used for automotive electrical components, it is often required that any one of the brush terminals be grounded after having been connected to an electrically conductive motor case.
The conventional method of grounding the miniature-motor body is as follows. A through-hole 8 through which a brush terminal piece 5 is protruded from the inside to the outside is provided on a case cover 7, as shown in FIG. 1 and the brush terminal piece 5 is passed through the through-hole 8 and fixedly fitted by inserting a leg of a split pin 13, made of an electrically conductive material and formed into an essentially U shape, into the through hole 8 from the inside of the case cover 7. After that, when the engaging surface of the case cover 7 is engaged with the motor case 1, another leg of the split pin 13 is forced onto the inside wall of the motor case 1, causing the brush having brush terminal piece 5 and the motor case 1 to be electrically connected.
Another conventional method is as Follows. A leg of the split pin 13 is spot-welded in advance to the motor case 1, and another leg of the split pin 13 is inserted into the through-hole 8 to fixedly fit and electrically connect the brush having the brush terminal piece 5 In FIG. 1, numeral 14 indicates a shouldered part with which the motor case 1 is engaged, and 15 a groove.
However, the construction in the former example, in which a leg of the split pin 13 is held by the motor case 1 and the case cover 7, is unstable in terms of electrical contact. The construction in the latter example, in which a leg of the split pin 13 is spot-welded to the motor case 1 can ensure stable electrical contact, but results in increased cost due to the spot-welding process involved. In addition, the spot welder has to be maintained at all times.